This invention relates to nickel/vanadium sputtering targets having high homogeneity, high purity and ultra-low levels of alpha emissions.
As a feature size of microcircuit structures are reduced, the quantity of critical electronic charge, which is used to represent a single xe2x80x9cbitxe2x80x9d (0 or 1) in binary code, is significantly decreased. A single alpha particle passing through the circuit element can adversely affect a minute amount of electronic charge and cause bit flips from one binary number to the other. The alpha particles are emitted from naturally occurring isotopes/impurities of raw materials that comprise the microchip.
Ni/7 wt. % V is the standard composition for use with direct current magnetron sputtering systems to deposit magnetic nickel. Nickel/vanadium (Ni/V) is employed as a barrier/adhesion layer for under-bump metals to support flip chips, or C4 (collapsed, controlled, chip connection) assemblies. The flip chips allow high I/O counts, good speed and electrical performance, thermal management, low profile, and the use of standard surface mount and production lines for assembly. Low alpha emitting nickel/vanadium sputtering targets are of paramount importance to thin film deposition with zero bit error in microcircuits. Nickel/vanadium sputtering targets currently available contain alpha emissions too high for satisfactory performance in microcircuits.
There is thus the need to develop a high purity, ultra-low alpha emission nickel/vanadium sputter target, and method for producing said target, sufficient for use in the thin film deposition of magnetic nickel on microcircuits and semi-conductor devices.
The present invention provides a nickel/vanadium sputter target having an alpha emission of equal or less than 10xe2x88x922 counts/cm2-hr, and preferably equal or less than 10xe2x88x924 counts/cm2-hr. To this end, and in accordance with the principles of the present invention, nickel and vanadium source materials of alpha emission equal or less than 10xe2x88x922 counts/cm2-hr are melted and cast under vacuum and low pressure atmosphere. The cast ingot is cut into a workpiece, rolled to final target thickness and annealed to form an ultra-low alpha emission sputter target.
In a further feature of the present invention, the nickel source material has a purity of at least about 99.98% and the vanadium source material has a purity of at least about 99.5%, such that the sputter target produced therefrom has a purity of at least 99.98%. Further, the target is cast, rolled, and annealed such that a uniform distribution of vanadium and impurities is obtained in the nickel.
These and other objects and advantages of the present invention shall become more apparent from the accompanying drawings and description thereof.